Abstract: The effects of seabuckthorn (Hippophae rhamnoides L. ), a nitrogen-fixing plant, on growth and biomass production in poplar plantations in subhumid-arid area of China were examined. In a 3 years project seabuckthorn was introduced into poplar stands of three different varieties (Populus cv. "Xiaohei", P. cv. "Zhaolin06" and P. euramericane cv. "N3016") in two different mixing designs (individual- or strip-mixing patterns). The positive effect of seabuckthorn on tree growth was found in all poplar plantations, irrespective of poplar variety or mixing pattern. The increases in diameter at breast height and mean height ranged from 6% to 38% and from 8% to 23%, respectively. In the individual-mixing pattern, the above-ground biomass of poplar trees was larger in mixed stands than in pure stands, but the reverse occurred in the strip-mixing patterns due to the lesser stock number per hectare. The aboveground net primary productivity was significantly larger (27 % to 113 % ) in mixed stands than in pure stands, regardless of poplar variety of mixing pattern. The increases was due largely to the contribution of the mixed seabuckthorn plants, accounting for 20% to 41 % of the total above-ground net productivity. Herbs comprised a negligible proportion of the total net productivity of stands in all three mixing patterns.

Key words: seabuckthorn, Tree growth, Biomass production, Poplar plantation